Gas turbines comprise a casing or cylinder for housing a compressor section, a combustion section, and a turbine section. A supply of air is compressed in the compressor section and directed into the combustion section. The compressed air enters the combustion inlet and is mixed with fuel. The air/fuel mixture is then combusted to produce high temperature and high pressure gas. This working gas then travels past the combustor transition and into the turbine section of the turbine.
The turbine section typically comprises rows of vanes which direct the working gas to the airfoil portions of the turbine blades. The working gas travels through the turbine section, causing the turbine blades to rotate, thereby turning the rotor. The rotor is also attached to the compressor section, thereby turning the compressor and also an electrical generator for producing electricity. High efficiency of a combustion turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is practical. The hot gas, however, may degrade the various metal turbine components, such as the combustor, transition ducts, vanes, ring segments and turbine blades that it passes when flowing through the turbine.
For this reason, strategies have been developed to protect such components from extreme temperatures such as the development and selection of high temperature materials able to withstand these extreme temperatures. For one, ceramic matrix composite (CMC) materials have been developed with a resistance to temperatures up 1200° C. CMC materials may include a ceramic or ceramic matrix, either of which may be reinforced with ceramic fibers. One issue with CMC materials, however, is that while CMC materials can survive temperatures in excess of 1200° C., they can only do so for limited time periods in a combustion environment without being cooled.
Cooling strategies have thus also been developed which may deliver a cooling fluid through the turbine component (e.g., blade, vane) in order to carry heat away from the component. For example, a cooling fluid may be flowed through an available inner volume of the component in order to provide adequate cooling to the component. It is appreciated that to provide sufficient cooling, the flow velocity of the cooling fluid must be at a sufficiently high flow velocity through the inner volume. Otherwise, the flow velocity may be too low to provide the desired cooling effects. However, such use of high volume of cooling fluid is not without detriment. Since the cooling fluid is not combusted or otherwise utilized to produce energy, the significant volume of cooling fluid used may result in significant material and operating costs for the associated gas turbine.